1. Field of the Invention
The present invention concerns a device for sealing a rotor shaft supported on a bearing mounted in the housing of an appliance for compressing or expanding a fluid, in particular a compressor or a tube expander of the type containing a housing and at least one rotor mounted therein, whereby the sealing device is situated between the rotor and the bearing around the rotor shaft and comprises at least two zero contact or frictionless seals.
2. Description of the Related Art
It is clear that a leak at the rotor shaft reduces the efficiency of such an appliance, but in some cases lubricant from the bearings, usually oil, ending up in the fluid of the appliance or fluid from the appliance ending up in the lubricant of the bearing represents an even greater disadvantage.
This is, for example, the case with compressors in which the bearings are lubricated with oil and oil-free compressed air is required.
With liquid-injected compressors, a lubricant is sprayed on the rotors which, in order to obtain such oil-free compressed gas, is not oil but, for example, water. Moreover, this lubricant must come into contact with the bearings or the oil for lubricating these bearings.
That is why in compressors and other appliances, devices for sealing a rotor shaft are applied which comprise several seals to guarantee an optimal sealing between the rotor and the bearing of the rotor shaft, both when the rotor is at rest and when it is rotating.
A screw-type compressor is described in WO 94/15100 which is equipped with devices for sealing the rotor shafts. Most devices consist of three zero contact seals with a ring-shaped chamber between the first and the second seal connecting to an output and a ring-shaped chamber between the second and the third seal onto which a compressed-air line is connected.
However, these known sealing devices do not provide a perfect sealing.